High frequency power amplifier, transmitter and mobile communication terminal using the power amplifier

ABSTRACT

A high frequency power amplifier maintains an excellent linearity regardless of a fluctuation of a load impedance and is downsized. The high frequency power amplifier detects an AC voltage amplitude at an output terminal of a final amplification stage transistor, and suppresses an input signal amplitude of a power amplifier when the voltage amplitude exceeds a predetermined threshold value.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Divisional application of U.S. application Ser.No. 11/430,172 filed May 9, 2006. Priority is claimed based on U.S.application Ser. No. 11/430,172 filed May 9, 2006, which claims priorityto Japanese Patent Application No 2005-138142 filed on May 11, 2005, thecontent of which is hereby incorporated by reference into thisapplication.

FIELD OF THE INVENTION

The present invention relates to a high frequency power amplifier usedin a high frequency mobile communication terminal and a transmitterusing the power amplifier, and more particularly to a high frequencypower amplifier that reduces a load impedance dependency of theamplifier characteristic, and a transmitter using the power amplifier.

BACKGROUND OF THE INVENTION

Japanese Patent Laid-Open No. 2000-341143 discloses an example of astructure of a conventional amplifier that reduces a dependency of thecharacteristic on a load impedance. The amplifier disclosed in JapanesePatent Laid-Open No. 2000-341143 conducts detection at plural points ona transmission line between a power amplifier and an antenna, detectsthe occurrence of a standing wave, that is, a mismatching of a load onthe basis of a difference between the detected levels, and limits aninput of the power amplifier.

Also, U.S. Pat. No. 6,720,831 discloses a structure that detects avoltage outputted from a final-stage transistor, and feeds back thedetected voltage to a bias voltage of the final-stage transistor.

SUMMARY OF THE INVENTION

In a power amplifier used for a high frequency mobile communicationterminal, a power can be reflected from an antenna toward the poweramplifier depending on a circumstance around the antenna. In the casewhere the power reflection thus occurs, it appears as if the loadimpedance from the amplifier with the antenna calculated fluctuates.When the load impedance viewed from the amplifier fluctuates, the loadimpedance of a transistor at an output stage that constitutes theamplifier also fluctuates with the result that the amplifier exhibitsthe characteristic different from the characteristic that has beenoriginally designed.

As one example, FIG. 1 schematically shows an influence of the loadimpedance fluctuation with respect to the gain of an amplifier, that isan input to output characteristic. Referring to FIG. 1, the axis ofabscissa is an input FRin to the amplifier, and the axis of ordinate isan output FRout of the power amplifier. A characteristic (2) exhibits anoriginal input to output characteristic, and there occurs acharacteristic (1) that is higher in the gain but lower in thesaturation output than the characteristic (2), or a characteristic (3)that is lower in the gain but higher in the saturation output than thecharacteristic (2), depending on the circumstance around the antenna.

Now, in a CDMA system that is required that the power amplifier operatesas a linear amplifier, the characteristic indicated by thecharacteristic (1) of FIG. 1 saturates the output at a lower output thanthe original linear maximum output, resulting in such a problem that adistortion that exceeds a permissible value of the system may occur.

To solve the above problem, there is an effective countermeasure that anisolator is inserted between the antenna and the power amplifier so thatthe reflected power from the antenna is not returned to the amplifier asshown in FIG. 5 of Japanese Patent Laid-Open No. 2000-341143. However,there arises such a problem that the isolator is expensive, and thepower amplifier is not downsized.

Also, in the conventional example shown in FIG. 1 of Japanese PatentLaid-Open No. 2000-341143, the voltage amplitudes at three differentpoints on an output matching circuit are measured, and a differencebetween the amplitudes of the standing waves that occur on thetransmission line is read to detect the occurrence of the reflectivewave to limit a control voltage level. However, the above structurerequires a transmission line length that is about ⅙ of the wavelengthand three voltage detector circuits, resulting in such a problem thatthe power amplifier is not downsized.

On the other hand, in an example shown in FIG. 2A of U.S. Pat. No.6,720,831, only one voltage detector is required because a voltage isdetected at an output end of a sensing transistor, however an object ofU.S. Pat. No. 6,720,831 is to prevent a power transistor from beingbroken down by detecting an overvoltage by a detector. In the case whereovervoltage is detected, a bias current of the power transistor isreduced. This example suffers from such a problem that there is thepossibility that the linearity of the power amplifier is deteriorated toproduce a distortion because the linearity of the power amplifier is nottaken into consideration.

The present invention has been made to solve the above problem, andtherefore an object of the present invention is to provide a highfrequency power amplifier that maintains an excellent linearityregardless of a fluctuation of the load impedance and is readilydownsized, and a transmitter using the power amplifier.

A representative example of the present invention will be stated below.

That is, according to the present invention, there is provided a highfrequency power amplifier that is used for a high frequency mobilecommunication terminal, the high frequency power amplifier comprising:at least one stage amplification stage that amplifies an input signalfrom a gain variable amplifier; an output matching circuit that isoutputted to an output side of the amplification stage; and a firstdetector unit that detects a voltage amplitude at a node between atransistor which constitutes the amplification stage and the outputmatching circuit to output the detected voltage amplitude as gaincontrol information of the gain variable amplifier.

According to the present invention, there can be provided a highfrequency power amplifier that maintains an excellent linearityregardless of a fluctuation of the load impedance, and a transmitterusing the power amplifier.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other objects and advantages of this invention will becomemore fully apparent from the following detailed description taken withthe accompanying drawings in which:

FIG. 1 is a schematic diagram showing an input to output characteristicof a power amplifier accompanying a fluctuation of a load impedance;

FIG. 2 is a circuit diagram showing a power amplifier according to afirst embodiment of the present invention;

FIG. 3 is a block diagram showing a transmitter according to a secondembodiment of the present invention;

FIG. 4A is a schematic diagram showing a dynamic load curve of atransistor due to a fluctuation of the load impedance according to thefirst or second embodiment of the present invention;

FIG. 4B is a diagram showing a relationship of a collector current tocollector voltage characteristic and Vdetout that is detected by acollector AC voltage detector unit according to the first or secondembodiment;

FIG. 5A is a diagram showing a distortion of a power amplifier and an ACvoltage amplitude of a collector end accompanying a phase fluctuation ofthe load impedance according to the first or second embodiment of thepresent invention;

FIG. 5B is an explanatory diagram, showing an operating characteristicaccording to the second embodiment of the present invention;

FIG. 6A is a diagram showing a structural example of a mobilecommunication terminal of a W-CDMA system according to a thirdembodiment of the present invention;

FIG. 6B is an explanatory diagram showing an operating characteristicaccording to the third embodiment of the present invention;

FIG. 7 is a circuit diagram showing a power amplifier according to afourth embodiment of the present invention;

FIG. 8 is a block diagram showing a transmitter using the poweramplifier according to the fourth embodiment of the present invention;

FIG. 9 is a schematic diagram showing a principle of the occurrence of adistortion accompanying a supply voltage fluctuation in the fourthembodiment of the present invention;

FIG. 10 is an explanatory diagram showing the operating characteristicaccording to the fourth embodiment of the present invention;

FIG. 11 a circuit diagram showing a power amplifier according to a fifthembodiment of the present invention;

FIG. 12 is a block diagram showing a transmitter using the poweramplifier according to the fifth embodiment of the present invention;

FIG. 13 is a circuit diagram showing a power amplifier according to asixth embodiment of the present invention; and

FIG. 14 is a block diagram showing a transmitter using the poweramplifier according to the sixth embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Now, a description will be given in more detail of preferred embodimentsof the present invention with reference to the accompanying drawings.

First Embodiment

First, a description will be given of a structure of a high frequencypower amplifier according to a first embodiment of the present inventionwith reference to FIG. 2. FIG. 2 is a circuit diagram showing a highfrequency power amplifier 10 according to the first embodiment of thepresent invention.

According to the first embodiment of the present invention, the highfrequency power amplifier 10 detects an AC voltage amplitude at anoutput terminal of a final amplification stage transistor, and outputs asignal for suppressing an input signal amplitude of the power amplifierwhen the detected voltage amplitude exceeds a predetermined specifiedvalue.

In other words, in the high frequency power amplifier 10 shown in FIG.2, reference numeral 1 and 3 denote input matching capacitors of theamplifier, and 2 is an input matching inductor. Reference numeral 100denotes an initial stage amplification transistor, 200 is a final stageamplification transistor, and 30 is a collector AC voltage detector unit(first detector unit). Reference numeral 202 is a MMIC (microwavemonolithic IC) that integrates the input matching capacitor 3, theinitial stage amplification transistor 100, the final stageamplification transistor 200, an interstage matching capacitor 251, andthe collector AC voltage detector unit 30 into one chip.

The power amplifier 10 includes an input terminal 4 to which an RF inputsignal RFin is inputted, an output terminal 5 from which an RF outputsignal RFout is outputted, and an output terminal 6 from which adetected output Vdetout of the AC voltage detector unit (first detectorunit) 30 is outputted. The detected output Vdetout of the first detectorunit is used as information for controlling the gain variable amplifierthat supplies the RF input signal to the input terminal 4.

A terminal 221 and a terminal 222 supply base biases Vbb1 and Vbb2 tothe initial stage amplification transistor 100 and the final stageamplification transistor 200, respectively. Reference numeral 231denotes an RF signal isolation inductor for base bias voltage supply ofthe initial stage amplification transistor 100, and 232 is an RF signalisolation inductor for base bias voltage supply of the final stageamplification transistor 200. Reference numeral 260 denotes a powersupply terminal that supplies a supply voltage Vcc, and 241 and 261 arechoke inductors for power supply of the initial and final amplificationtransistors, respectively. Reference numeral 242 and 262 denote bypasscapacitors for supply voltage stabilization, respectively.

The collector AC voltage detector unit 30 includes a voltage detectiondiode 300, a voltage detection resistor 301, and a voltage detectioncapacitor element 302. An output matching circuit 280 of the amplifieris made up of output matching capacitors 281, 282, and 283, and outputmatching transmission lines 285 and 286.

According to this embodiment, the first detector unit 30 detects thevoltage amplitude Vdetout at a node between the final stageamplification transistor at the amplification stage and the outputmatching circuit, and outputs the detected voltage amplitude as controlinformation of the gain variable amplifier that supplies the RF inputsignal to the input terminal 4. The use of the detected output Vdetoutmakes it possible to control the gain of the gain variable amplifieraccording to the output voltage amplitude Vdetout of the amplificationtransistor which corresponds to a fluctuation of the load impedance. Asa result, the input signal amplitude of the power amplifier, that is,the output of the gain variable amplifier can be controlled so that theoutput of the high frequency power amplifier is always in a linearoperation region where there is no distortion of the output, therebymaking it possible to suppress the distortion from occurring at the timeof fluctuating the load impedance. Since it is unnecessary to insert anisolator between the antenna and the power amplifier, the costs are notincreased.

Also, the transistors at the respective stages which constitute the highfrequency power amplifier according to this embodiment is a self biassystem that allows the bias current to increase upon inputting the RFinput signal RFin. As a result, even when the distortion occurs at thetime of fluctuating the load impedance, the amplitude of the RF inputsignal is reduced without reducing the bias currents of the transistorpower amplifiers at the respective stages. In other words, the amplitudeof the RF input signal RFin is in an operating range of the self biassystem which corresponds to the RF input voltage. For that reason, whenthe amplitude of the RF input signal is reduced, the bias current isalso reduced according to the reduced RF input signal. From thisviewpoint, the transistors at the respective stages operate within theregular operation range even when the distortion occurs at the time offluctuating the load impedance. As a result, the operation in the linearregion is ensured.

Also, since the output terminal 6 of the collector AC voltage detectorunit 30 is connected to the collector of the final stage amplificationtransistor 200, the output of the collector AC voltage detector unit 30is coupled with the information on the supply voltage, which iseffective in suppression of the distortion.

Second Embodiment

A description will be given of an example of a transmitter using thepower amplifier of the first embodiment according to a second embodimentof the present invention with reference to FIGS. 3 to 5C.

First, FIG. 3 is a block diagram showing a structural example of atransmitter to which the power amplifier shown in FIG. 2 is applied. Thepower amplifier 10 has an RF input signal RFin terminal 4 connected toan external gain variable amplifier 12, and has an RF output signalRFout terminal 5 connected to an antenna 14. Also, the power amplifier10 has a terminal 6 that outputs an AC voltage amplitude output Vdetoutof the collector AC voltage detector unit 30 in the power amplifier 10connected to a control circuit 18 through an A/D converter 16. Thecontrol circuit 18 is disposed within the transmitter, more preferablywithin a base band control circuit (base band IC).

A high frequency transmit signal Fr0 obtained by modulating a carrierwave in phase on the basis of information to be transmitted is inputtedto the gain variable amplifier 12, then amplified by the amplifier, andinputted to the power amplifier 10 as the high frequency signal RFin.The signal is further amplified by the power amplifier 10, outputted asthe high frequency signal RFout, and drives the antenna 14 and conductstransmission. The detected output Vdetout is used as information forgain control of the gain variable amplifier 12. In other words, thecontrol circuit 18 controls the gain of the gain variable amplifier 12according to the output Vdetout of the AC voltage amplitude that isdetected by the collector AC voltage, detector unit 30.

According to this embodiment, the control circuit 18 monitors Vdetout asthe information for gain control, and generates such a control signal asto limit the gain of the gain variable amplifier 12 when a conditionunder which a distortion occurs in the output of the power amplifier 10is satisfied, that is, when the output voltage amplitude of theamplification transistor exceeds a predetermined threshold value. Inother words, the control circuit 18 controls the gain of the gainvariable amplifier 12 according to the output voltage amplitude of theamplification transistor 200. When the load impedance is equal to orlower than a normal range, the gain of the gain variable amplifier 12 isset on the basis of a given parameter. When the condition under whichthe distortion occurs in the output of the power amplifier 10 issatisfied, that is, when the output voltage amplitude Vdetout of theamplification transistor 200 exceeds a predetermined threshold valuewith an increase in the load impedance, the gain of the gain variableamplifier 12 is limited to a gain lower than a normal gain of the gainvariable amplifier 12. As a result, the high frequency power amplifier10 operates in a region where no distortion occurs in the outputthereof.

With the above operation, the high frequency amplifier 10 maintainsexcellent linearity regardless of the fluctuation of the load impedance.As a result, the output of the gain variable amplifier 12, that is, theinput signal amplitude of the power amplifier is so controlled as to bein a region where no distortion occurs in the output of the highfrequency power amplifier, thereby making it possible to suppress theoccurrence of distortion at the time of fluctuating the load impedance.

According to the structure of the power amplifier according to the firstembodiment or the transmitter according to this embodiment, theoccurrence of distortion can be suppressed at the time of fluctuatingthe load impedance. Hereinafter, this feature will be described in moredetail.

FIG. 4A is a diagram schematically showing a collector current tocollector voltage characteristic of the output stage transistor in thepower amplifier 10, and a relationship between a voltage Vc and acollector current Ic at the collector terminal in the RF large signalamplifying operation, that is a dynamic load curve. A real part of theload impedance corresponds to a slope of the dynamic load curve shown inFIG. 4A, and therefore the collector current to collector voltagecharacteristics (1) to (3) shown in FIG. 1 approximately correspond tothe collector current to collector voltage characteristics (1) to (3)shown in FIG. 4A.

FIG. 4B shows a relationship of collector current to collector voltagecharacteristics (1) to (3), and Vdetout (1) to (3) that are detected bythe collector AC voltage detector unit 30 in correspondence with thosecollector current to collector voltage characteristics.

A distortion is difficult to occur in the collector current to collectorvoltage characteristics (2) and (3) of FIG. 4A, but a dynamic load curveis distort distorted without drawing an oval at a lower voltage side in(1). Since the dynamic load curve is thus distorted, the outputsaturation occurs at a lower output than the original input to outputcharacteristic (2) as indicated by (1) in FIG. 1.

In the dynamic load curve (1) of FIG. 4A, the dynamic load curve isdistorted at the lower voltage side, and the load curve extends towardthe higher voltage side. On the other hand, in the dynamic load curve(3) of FIG. 4A, the voltage remains at a low voltage. From thisviewpoint, it is estimated that there is a correlation between theoccurrence of a distortion and an RF voltage at the collector end.

The output matching circuit 280 of the power amplifier 10 is normallymatched with the impedance of 50 ohms. When a load that is differentfrom 50 ohms is connected to the power amplifier 10, a reflection occursfrom the load. As a result, the input to output characteristic isexhibited as indicated by (1) and (3) of FIG. 1, and a distortion mayoccur in the output as described above.

In the mobile terminal of the W-CDMA system, a reflection from theantenna is attenuated due to the loss of a part that is inserted betweenthe power amplifier 10 and the antenna 14, and the mismatching of theoutput RFout becomes about 4:1 or less in a voltage standing wave ratio(VSWR) at the output terminal 5 of the power amplifier.

In FIG. 5A, the AC voltage amplitude Vdetout at the collector end of thetransistor 200 of the amplifier 10 shown in FIG. 2, and an AdjacentChannel Leak power Ratio (ACLR) that is an index indicative of thedistortion of the W-CDMA signal are obtained by a circuit simulation inthe case of VSWR=4:1. In this simulation, in order to set the VSWR to4:1, the load impedance is set to 200 ohms, and a transmission line isinserted between the load and the power amplifier 10 to represent aphase of the reflection from the antenna 14. The phase rotation of thetransmission line changes from 0° to 180° with the results that thephase rotation of 0° to 360° there and back is conducted, and all ofcases are conducted. The characteristics when the simulated poweramplifier has a load of 50 ohms are 27.5 dBm in the output power whenthe supply voltage Vcc is 3.5 V and the input power is 1 dBm, and ACLRat that time is −42 dBc.

Referring to FIG. 5A, an upper trace is the AC voltage amplitudeVdetout, and a lower trace is the adjacent channel leak power ratioACLR. It is apparent from FIG. 5A that there is an excellent correlationwith the output Vdetout of the AC voltage amplitude to the adjacentchannel leak power ratio ACLR. In a region of Vdetout <3 V indicated byarrows in FIG. 5A, ACLR is −34 dBc even at worst, which is lower than−33 dBc which is the worst value of ACLR of 3GPP standard that is thestandard of the W-CDMA system. Thus, it is found that the control unit18 of FIG. 3 controls the gain variable amplifier 12 so as to satisfyVdetout<3 V with Vdetout=3 V as a threshold voltage, to thereby realizethe operation that satisfies the ACLR standard.

In this embodiment, the information that is obtained by the firstdetector unit 30 allows the gain of the gain variable amplifier 12 to becontrolled according to the output voltage amplitude of theamplification transistor. Therefore, when the load impedance is large,the output of the gain variable amplifier. 12, that is, the input signalamplitude of the power amplifier is suppressed to a value P2 that issmaller than P1, as shown in FIG. 5B. For that reason, the poweramplifier operates in a region where no output distortion occurs at afurther left side than P2.

In fact, the threshold voltage is set in a range where no outputsuppression signal occurs with respect to the gain variable amplifier 12under the specified output in the normal operation of the matching of 50ohms, thereby making it possible to operate in a lower distortion stateat the time of the load impedance fluctuation. This fact is applied toother embodiments that will be described later.

Also, in the case where the gain variable amplifier 12 is structured tohave multiple stages and the load impedance is large, the gain as awhole can be made to be a predetermined value by limiting each gain ofeach stage.

When the inventors actually made the power amplifier 10 shown in FIG. 2,composed a transmit system shown in FIG. 3, experimented, and optimizedthe above threshold value, ACLR<−36 dBc was obtained under the loadfluctuation condition of up to VSWR=4:1.

Also, according to this embodiment, a circuit configuration for ensuringthe linearity is simple, and an influence of an addition of the abovecircuit configuration on the size and costs of the high frequency poweramplifier or the transmitter using the high frequency power amplifier issmall. In other words, in the configuration of this embodiment, acircuit that is added to the normal power amplifier 10 is only a voltagedetector unit indicated by reference numeral 30 in FIG. 2. In thevoltage detector unit 30, the voltage detection diode 300 can berealized by diode connection of the transistor. Also, both of thevoltage detection resistor 301 and the capacitor 302 can be produced bya normal MMIC process. As a result that the voltage detector circuit 30is incorporated into the power amplifier for the W-CDMA, an increase inthe MMIC chip area stays within 5%.

As described above, according to the present invention, the AC voltageamplitude Vdetout at the output terminal of the final amplificationstage transistor 200 as shown in FIG. 4B is detected, and when acondition under which the distortion occurs is satisfied, that is, whenthe output voltage amplitude of the amplification transistor exceeds apredetermined threshold value, since a signal that suppresses the inputsignal amplitude of the power amplifier is outputted, the operationregion of the power amplifier is limited. As a result, excellentlinearity can be held regardless of the fluctuation of the loadimpedance. Moreover, an increased area of the MMIC chip area is veryslight as compared with the normal power amplifier 10, and it ispossible to provide a high frequency power amplifier that is small inthe size and low in the costs, and a mobile communication terminal usingthe power amplifier.

Third Embodiment

A third embodiment of the present invention will be described withreference to FIGS. 6A and 6B. In this embodiment, the high frequencypower amplifier shown in FIG. 2 or 3 is applied to a mobilecommunication terminal of the W-CDMA system.

A mobile communication terminal shown in FIG. 6A includes a highfrequency signal processor circuit that has a modulator and demodulatorcircuit which is capable of modulating and demodulating the W-CDMAsignal, and is brought into a semiconductor integrated circuit. That is,the mobile communication terminal includes an electronic device 600, ahigh frequency power amplifier (power module) 700, and a front endmodule 800.

In the electronic device 600 corresponding to the base band controlcircuit (base band IC) shown, in FIG. 3, a modulator and demodulatorcircuit which is capable of modulating and demodulating the W-CDMAsignal, and a base band circuit 610 that generates I and Q signals orprocesses the I and Q signals that have been extracted from a receivesignal on the basis of transmit data (base band signal) are incorporatedinto one package together with a band pass filter (BPF1) 650 thatremoves a high frequency component from the transmit signal, and a bandpass filter (BPF2) 651 that removes an unnecessary wave from the receivesignal.

The electronic device 600 according to this embodiment has, formed onone semiconductor chip: the base band circuit 610 including a terminalcontrol unit 620 that processes the high frequency signal; a receiverunit 630; a transmitter unit 640; transmit variable gain amplifiers(GCA) 611 and 661 that amplify the transmit signal that has beenmodulated; a mixer (Tx-MIX) 652 that up-converts the transmit signalthat has been amplified; a low noise amplifier (LNA) 612 that amplifiesthe receive signal; and a mixer (Rx-MIX) 653 that down-converts thereceive signal that has been amplified.

In addition, the electronic device 600 is equipped with a nonvolatilememory 613 that stores table data that is referred to at the time ofoutputting a control current, and DA converter circuits 614 and 615 thatsubject data that has been read from the nonvolatile memory 613 andprocessed by the terminal control unit 620 of the base band circuit 610to DA conversion, and output the converted data as analog currents.

The high frequency power amplifier (power module) 700 has a highfrequency power amplifier 710 that amplifies the high frequency signal,a matching circuit 714, an A/D converter 680, a bias control circuit720, and a collector AC voltage detector unit (first detector unit) 730mounted on one ceramic substrate.

The radio communication system also includes a switch (DUPLEXER) 810that is disposed in the front end module 800 for changing over transmitand receive, an output detector circuit (PDT) 740 made up of a couplerthat detects an output level of the transmit signal which is outputtedfrom the power module 700, a filter (LPF) 830 that removes noise such asa higher harmonic wave included in the transmit signal, and an automaticpower control circuit (APC circuit) 670 that generates an output controlsignal Vapc with respect to the transmit variable gain amplifiers (GCA)611 and 661 within the electronic device 600 on the basis of the outputdetection signal from the detector circuit 740 and the power controlsignal PCS from the base band circuit 610.

In the radio communication system according to this embodiment, thecontrol current and the mode control signal with respect to the biascircuit 720 within the power module 700 are supplied from the base bandcircuit 610 of the electronic device 600. Also, a reference voltage thatis inputted to the voltage to current converter circuit and the offsetcurrent adder circuit within the bias circuit 720 is also supplied fromthe base band circuit 610.

In this embodiment, the output control signal that is outputted from theautomatic power control circuit 670 which controls the output level issupplied to the transmit variable gain amplifiers 611 and 661 within theelectronic device 600 in a state where the gains of the initial stageamplification transistor and the final stage amplification transistor inthe power amplifier 710 are held constant according to the controlcurrents Ic1 and Ic2 which are supplied from the base band circuit 610.Then, the gains of the transmit variable gain amplifiers 611 and 661 arecontrolled according to the output control signal Vapc. As a result, theoutput power of the power amplifier 710 is changed under the control. Apower compensation function is given to the bias circuit 720 thatsupplies a bias to the power amplifier 710, thereby making it possibleto maintain the gain of the power amplifier 710 substantially constanteven if the supply voltage changes due to the charge or consumption of abattery. As a result, the receive band noise is capable of satisfyingthe standard. Also, the table data that is a base for generating thepower control signal PCS that is supplied to the automatic power controlcircuit 670 according to the output request level which is supplied froma base station is also stored in the nonvolatile memory 613.

In this embodiment, a down receive signal from the base station isreceived by the antenna 14 of the mobile communication terminal; andthen inputted to the low noise amplifier (LNA) 612 through thetransmit/receive separation filter (DUPLEXER) 810. Thereafter, thedownload signal is down-converted by the mixer 653 through the band passfilter 651, adjusted to a desired level by the receive variable gainamplifier, and then converted into the receive base band signal. Thereceive base band signal is extracted by the receiver unit 630. Also,the receive base band signal is branched and transmitted to the gaincontrol unit 62.1 that generates the receive gain control signal whichallows the receive base band signal to be a desired constant level,which controls the receive variable gain amplifier.

The transmit base band signal that has been generated by the transmitterunit 640 is converted into a transmit intermediate frequency through anorthogonal converter, and the transmit level is adjusted by the variablegain amplifier 611. Thereafter, the adjusted signal is amplified into adesired transmit output by the power amplifier 710 through the mixer 652and the base band filter 650, and then emitted as an up transmit signalfrom the antenna 14 through a directional coupler and thetransmit/receive separation filter (DUPLEXER) 810. Also, the transmitgain control signals Va1 and Va2 that control the gains of the variablegain amplifier 611 and 661 are supplied to the transmit variable gainamplifiers 611 and 661 through the limiter 622, and control is made sothat the gains of the transmit variable gain amplifiers 611 and 661 arenot excessive. The limit value is set by the terminal control unit 620.

As the adjustment of the transmit levels in the transmit variable gainamplifiers 611 and 661, in order to keep the quality of an up link ofthe base station, the mobile communication terminal transmits with alarge power when the mobile communication terminal is apart from thebase station, and the transmit power is lowered when the mobilecommunication terminal is close to the base station. The base stationmonitors the quality of the up link signal, and then instructs the downlink signal so as to increase the transmit power of the mobilecommunication terminal when the quality of the up link signal isdeteriorated. The base station also instructs the down link signal so asto decrease the transmit power of the mobile communication terminal whenthe quality of the up link signal is equal to or higher than a givenquality. The mobile communication terminal extracts those information inthe receiver unit 630, and transmits those information to the gaincontrol unit 621 of the terminal control unit 620. Also, the gaincontrol information of the gain variable amplifiers 611 and 661 whichare detected by the collector AC voltage detector unit 730 is alsotransmitted to the gain control unit 621. The gain control unit 621generates the transmit gain control signal Va according to thoseinformation.

The transmit gain control signals Va1 and Va2 control the gains of thetransmit variable gain amplifiers 611 and 661. The transmit gain controlsignals Va1 and Va2 are supplied to the transmit variable gainamplifiers 611 and 661 through the limiter 622 where control is made sothat the gains of the transmit variable gain amplifiers 611 and 661 arenot excessive. This, is because in the case where the up transmit powerthat is requested from the base station is too large, the transmitsignal is prevented from being distorted by the power amplifier 710 tospread the spectrum toward the adjacent frequencies and interfere withthe adjacent frequencies.

To achieve this, the limiter 622 has the input to output characteristicas shown in FIG. 6B. For example, the limiter 622 conducts limiteroperation that limits a limiter input that is equal to or higher than apredetermined value to a limit value (=limit−1) on the basis of thebasic information such as the channel frequency information. The limitvalue determines the maximum transmit power of the mobile communicationterminal.

In this embodiment, the gain control information of the gain variableamplifiers 611 and 661 is transmitted to the gain control unit 621 ofthe terminal control unit 620 in addition to the basic information. Withthis operation, in the case where Vdetout that is detected by thecollector AC voltage detector unit 730 to exceed the given value even ifthe maximum transmit power is within the limit value (=limit−1), thelimit value is changed to a smaller value (=limit−2) to suppress themaximum transmit power.

According to this embodiment, it is possible to provide the mobilecommunication terminal of the W-CDMA system which maintains excellentlinearity regardless of the fluctuation of the load impedance, and isreadily downsized.

Fourth Embodiment

Now, a description will be given of the structure of a fourth embodimentof the present invention with reference to FIGS. 7 to 10. A poweramplifier 10 shown in FIG. 7 is changed in the power amplifier 10 shownin FIG. 2 in such manner that an output of a collector AC voltageamplitude detector circuit (first detector unit) 30 and a supply voltageVcc are inputted to a signal processor 305, and a signal processingresult from the signal processor 305 is outputted as an output Vdetoutof the AC voltage amplitude.,

FIG. 8 is a block diagram showing the structure of a transmitter in amobile terminal of the W-CDMA system to which the power amplifier 10shown in FIG. 7 is applied. The power amplifier 10 has an input terminal4 of the high frequency signal RFin connected to an external gainvariable amplifier 12 and an output terminal 5 of the high frequencysignal RFout connected to an antenna 14. Also, a supply terminal 260that is connected with the supply voltage Vcc is connected to a controlcircuit (base band IC) 18 through an A/D converter 161. Further, an ADvoltage amplitude output Vdetout that is outputted from an outputterminal 6 of a collector AD voltage detector unit 30 in the poweramplifier 10 is inputted to the control circuit (base band IC) 18through an A/D converter 162.

The power amplifier 10 is inputted with the high frequency signal RFinobtained by modulating a carrier wave in phase, and the amplified highfrequency signal RFout drives the antenna 14 to conduct transmission.The control circuit 18 controls the gain of the gain variable amplifier12 according to the supply voltage Vcc and the output Vdetout of the ACvoltage amplitude.

As shown in FIG. 9, there is a case in which a distortion occurs whenthe supply voltage Vcc is reduced even under the condition where nodistortion occurs in the supply voltage during the normal operation ofthe power amplifier 10. FIG. 10 shows this condition by the input tooutput characteristic of the power amplifier 10. The saturated output islowered with a reduction of the supply voltage, and the linearity islost at a lower output so that the distortion can occur.

In this embodiment, in order to suppress the occurrence of distortiondue to the supply voltage reduction, the supply voltage and thecollector AC voltage amplitude are signal processed, to thereby allowthe gain suppression threshold value of the gain variable amplifier tochange according to the supply voltage, and the gain variable amplifier12 is controlled so that the input signal amplitude of the poweramplifier 10 becomes equal to or lower than a predetermined value. Withthe above operation, the occurrence of the distortion at the time of thesupply voltage reduction is suppressed. Also, since the self bias systemby which the bias current changes according to the amplitude of the RFinput signal RFin of the power amplifier is applied, the bias current isreduced as the amplitude of the RF input signal is reduced. As result,the ensuring of the linear operation region is further facilitated.

As a comparative example, in the case where the amplifier 10 that hasacquired the characteristic of FIG. 5A is made to operate while theabove threshold voltage is constantly kept at 3 V, and the supplyvoltage is reduced from the standard voltage of 3.5 V, the worst valueof the ACLR exceeds −33 dBc when the supply voltage is reduced down to3.2 V, and the 3GPP standard is not satisfied.

On the other hand, in the case where the signal processor circuitaccording to this embodiment is optimized, even if the supply voltage isreduced down to 2.8 V, the worst value of the ACLR remains at −36 dBc,and a margin can be taken with respect to the 3GPP standard.

Fifth Embodiment

A description will be given of a high frequency power amplifieraccording to a fifth embodiment of the present invention with referenceto FIGS. 11 and 12. As shown in FIG. 11, the fifth embodiment includes asecond detector unit 40 in addition to the collector AC voltage detectorunit (first detector unit) 30 shown in FIG. 2. That is, a directionalcoupler 306 is provided in the output matching circuit as the seconddetector unit 40, and its output signal is detected by the detectorcircuit 40 and outputted from a terminal 403 as Cplout. The seconddetector section 40 is made up of a voltage detection diode 400, avoltage detection resistor 401, and a voltage detection capacitorelement 402.

FIG. 12 is a block diagram showing the structure of a transmitter in amobile terminal of the W-CDMA system to which the power amplifier 10shown in FIG. 11 is applied. The power amplifier 10 has a signal inputterminal RFin 4 connected to an external gain variable amplifier 12 andan output terminal RFout 5 connected to an antenna 14. Also, an ACvoltage amplitude output Vdetout that is outputted from the outputterminal 6 of the collector AC voltage detector unit 30 in the poweramplifier 10 is connected to a control circuit (base band IC) 18 throughan A/D converter 162. Further, a terminal 403 of the output signalCplout of the directional coupler 306 in the output matching circuit isconnected to the control circuit (base band IC) 18 through an A/Dconverter 163 as a second detector unit 40.

The power amplifier 10 is inputted with the high frequency signal RFinobtained by modulating a carrier wave in phase according to informationto be transmitted, and the amplified high frequency signal RFout drivesthe antenna 14 to conduct transmission. The control circuit 18 controlsthe gain of the gain variable amplifier 12 according to the supplyvoltage Vcc and the output Vdetout of the AC voltage amplitude.

The characteristic fluctuation of the amplifier accompanying the signalload impedance fluctuation is substantially symmetrical with respect tothe phase of the load impedance as shown in FIG. 5A. In FIG. 5A, itssymmetrical axis is 30° and 120° in a ½ phase angle value. Accordingly,the output Cplout from the directional coupler 306 for detecting theelectric power of a traveling wave that progresses from the poweramplifier 10 toward the antenna 14 is obtained by the second detectorunit. Also, the information on the output Vdetout of the first detectorunit that detects the AC voltage at the collector terminal which isobtained by superimposing the traveling wave on the reflective wave fromthe antenna 14, thereby making it possible to know the traveling waveamplitude and the amplitude and phase of the reflective wave. Therefore,those signals are processed with the result that not only the distortionof the amplifier is reduced which is a primary object of the presentinvention, but also functions of a higher level can be realized.

For example, in a state (3) of FIG. 4A, the collector current of thefinal stage transistor 200 becomes excessive due to the fluctuation ofthe load impedance. However, the use of the circuit according to thepresent invention makes it possible to identify a condition under whichthe collector current becomes excessive according to the information onthe traveling wave output, the amount of reflection of the reflectivewave, and the phase of the reflective wave. In this case, the gain ofthe gain variable amplifier 12 is reduced so that flow of the excessivecurrent can be suppressed. Also, since the amount of reflection from theantenna 14 can be detected according to the above information, it ispossible to know the radiation from the antenna. With the aboveoperation, the amount of radiation from the antenna is kept constant inan output range where no distortion occurs even if the condition aroundthe antenna is changed, thereby making it possible to reduce thepossibility of disconnecting the link which is attributable to theradiation output fluctuation due to a change in the condition around theantenna under the control.

Sixth Embodiment.

FIGS. 13 and 14 show a high frequency amplifier according to a sixthembodiment of the present invention.

A high frequency amplifier shown by a circuit diagram of FIG. 13 is ahigh frequency amplifier that is capable of detecting both of the supplyvoltage output described in the fourth embodiment and the traveling waveoutput using the directional coupler described in the fifth embodiment,which has both of the features of the fourth embodiment and the fifthembodiment.

FIG. 14 is a block diagram showing the structure of a transmitter usinga power amplifier according to this embodiment. In other words, the gainof the gain variable amplifier is controlled according to thefluctuation of the supply voltage by using an optimum threshold valuethat is capable of suppressing the distortion to make the output of theterminal maximum while maintaining the signal quality. Also, theinformation on the second detector unit is used to maintain theradiation output from the antenna constant even in the case where areflection occurs in the antenna at the time of the low output where thedistortion leads to no problem, thereby making it possible to improvethe stability of the link connection at the terminal.

As was described above, according to the respective embodiments, it ispossible to provide a high frequency power amplifier that maintains theexcellent linearity regardless of the fluctuation of the load impedanceand is readily downsized, and a transmitter using the high frequencypower amplifier.

It is needless to say that the same effects can be obtained by applyingthe high frequency amplifier and the transmitter described in the fourthto sixth embodiments to the mobile communication terminal of the W-CDMAsystem shown in FIG. 6.

Also, the present invention can be applied to an EDGE (Enhanced Data GSMEnvironment) which is one of the data transmission techniques using theGSM system or the TDMA system, likewise.

The foregoing description of the preferred embodiments of the inventionhas been presented for purposes of illustration and description. It isnot intended to be exhaustive or to limit the invention to the preciseform disclosed, and modifications and variations are possible in lightof the above teachings or may be acquired from,practice of theinvention. The embodiments were chosen and described in order to explainthe principles of the invention and its practical application to enableone skilled in the art to utilize the invention in various embodimentsand with various modifications as are suited to the particular usecontemplated. It is intended that the scope of the invention be definedby the claims appended hereto, and their equivalents.

1. A mobile communication terminal, comprising: a base band circuithaving a limiter that determines a maximum transmit power of the mobilecommunication terminal; a transmit variable gain amplifier that receivesthe control signal from the base band circuit; a power amplifier thatamplifies a transmit signal from the transmit variable gain amplifier; afront end module coupled to the power amplifier; and an antenna coupledto-the front end module, wherein the power amplifier includes twoamplification stages for amplifying an input signal from a gain variableamplifier, wherein the power amplifier includes: a first amplificationstage; a second amplification stage comprising a transistor, andelectrically coupled to the first amplification stage; an outputmatching circuit that is coupled to an output side of the secondamplification stage; and a first detection unit for detecting a voltageamplitude at a node between the transistor of the second amplificationstage and the output matching circuit, and outputting the voltageamplitude as a first signal of gain control information of the gainvariable amplifier, detecting a supply voltage being supplied to thesecond amplification stage, and outputting the supply voltage as asecond signal of the gain control information of the gain variableamplifier, and wherein the gain variable amplifier is controlled basedon the gain control information so as to limit a gain of the gainvariable amplifier, upon the voltage amplitude exceeding a predeterminedthreshold voltage.
 2. The mobile communication terminal according toclaim 1, wherein the first detection unit includes a voltage detectiondiode that is connected to a collector of the transistor of the secondamplification stage, and a voltage detection resistor and a capacitorthat are coupled to the voltage detection diode.
 3. The mobilecommunication terminal according to claim 2, further comprising a seconddetection unit having a directional coupler that is disposed within theoutput matching circuit or between the output matching circuit and theoutput terminal, and wherein the second detection unit outputs an outputsignal of the directional coupler as a third signal of the gain controlinformation of the gain variable amplifier.
 4. The mobile communicationterminal according to claim 3, wherein an input matching capacitor andan interstage matching capacitor that are coupled to the transistor ofthe second amplification stage, the transistor of the secondamplification stage, and the first detection unit are integrated on onechip.
 5. The mobile communication terminal according to claim 2, whereinan input matching capacitor and an interstage matching capacitor thatare coupled to the transistor of the second amplification stage, thetransistor of the second amplification stage, and the first detectionunit are integrated on one chip.
 6. The mobile communication terminalaccording to claim 2, wherein the transistor of the second amplificationstage is of a self bias system in which a bias current with respect tothe power amplifier changes according to an RF input voltage.